Tool: Minor fix about comments.

Signed-off-by: Sherry Zhang <sherry.zhang2@arm.com>
Change-Id: Iea0def04dc8fd5665bb4f854b7fdedfefd3b2a62
diff --git a/tools/tfm_parse_manifest_list.py b/tools/tfm_parse_manifest_list.py
index 773a160..8b7afa1 100644
--- a/tools/tfm_parse_manifest_list.py
+++ b/tools/tfm_parse_manifest_list.py
@@ -27,7 +27,7 @@
 TFM_ROOT_DIR = os.path.join(sys.path[0], '..')
 OUT_DIR = None # The root directory that files are generated to
 
-# PID[0, TFM_PID_BASE] are reserved for TF-M SPM and test usages
+# PID[0, TFM_PID_BASE - 1] are reserved for TF-M SPM and test usages
 TFM_PID_BASE = 256
 
 # variable for checking for duplicated sid